The extensive data storage needs of modem computer systems require large capacity mass data storage devices. A common storage device is the rotating magnetic disk drive.
A disk drive typically contains one or more smooth, flat disks which are rigidly attached to a common spindle. The disks are stacked on the spindle parallel to each other and spaced apart so that they do not touch. The disks and spindle are rotated in unison at a constant speed by a spindle motor.
Each disk is formed of a solid disk-shaped base or substrate, having a hole in the middle for the spindle. The substrate is commonly aluminum, although glass, ceramic, plastic or other materials are possible. The substrate is coated with a thin layer of magnetizable material, and may additionally be coated with a protective layer.
Data is recorded on the surfaces of the disks in the magnetizable layer. To do this, minute magnetized patterns representing the data are formed in the magnetizable layer. The data patterns are usually arranged in circular concentric tracks. Each track is further divided into a number of sectors. Each sector thus forms an arc, all the sectors of a track completing a circle.
A movable actuator positions a transducer head adjacent the data on the surface to read or write data. Although earlier disk drive designs used a linear actuator, which moved back and forth on straight rails, most disk drives now being produced use a rotary actuator, which pivots about an axis. The rotary actuator may be likened to the tone arm of a phonograph player, and the head to the playing needle.
There is one transducer head for each disk surface containing data. The transducer head is an aerodynamically shaped block of material (usually ceramic) on which is mounted a magnetic read/write transducer. The block, or slider, flies above the surface of the disk at an extremely small distance as the disk rotates. The close proximity to the disk surface is critical in enabling the transducer to read from or write to the data patterns in the magnetizable layer. Several different transducer designs are used, and in some cases the read transducer is separate from the write transducer.
A rotary actuator typically includes a solid block near the axis having comb-like arms extending toward the disk, a set of thin suspensions attached to the arms, and an electro-magnetic motor on the opposite side of the axis. The transducer heads are attached to the suspensions, one head for each suspension. The actuator motor rotates the actuator to position the head over a desired data track. Once the head is positioned over the track, the constant rotation of the disk will eventually bring the desired sector adjacent the head, and the data can then be read or written.
As computer systems have become more powerful, faster, and more reliable, there has been a corresponding increase in demand for improved storage devices. These desired improvements take several forms. It is desirable to reduce cost, to increase data capacity, to increase the speed at which the drives operate, to reduce the electrical power consumed by the drives, and to increase the resilience of the drives in the presence of mechanical shock and other disturbances.
In particular, there is a demand to reduce the physical size of disk drives. To some degree, reduction in size may serve to further some of the above goals. But at the same time, reduced size of disk drives is desirable in and of itself. Reduced size makes it practical to include magnetic disk drives in a range of portable applications, such as laptop computers, mobile pagers, and "smart cards".
An example of size reduction is the application of the PCMCIA Type II standard to disk drives. This standard was originally intended for semiconductor plug-in devices. With improvements to miniaturization technology, it will be possible to construct disk drives conforming to the PCMCIA Type II standard.
In order to shrink the size of disk drives, every component must be reduced in size as much as possible. Additionally, because the PCMCIA Type II standard, as well as many other small form factor drives, are intended for portable use, it is necessary that such devices be capable of tolerating a high mechanical shock, such as might occur when a disk drive is dropped onto a hard floor. Conventional drives designed for desktop applications have been susceptible to shock damage. With portable applications becoming more significant, there is a need to find new design techniques to permit reduced size and power consumption, to make assembly of miniaturized components practical, and prevent the drive from being damaged when exposed to mechanical shock.
Conventionally, the rotatable disk spindle assembly and the rotary actuator assembly are supported by sets of ball bearings housed in annular races. Typically, there are two sets of bearings for the disk spindle and two for the rotary actuator, the two sets supporting a particular assembly being axially separated to provide greater stability. The number of parts makes it increasingly difficult to shrink the size of the bearing assembly. Additionally, when this design is miniaturized for a small form factor disk, individual balls become extremely small and susceptible to mechanical shock. Finally, multiple balls generate significant bearing drag and mechanical hysteresis, the latter being particularly troublesome for rotary actuators, which frequently alter direction.
It has been proposed to address problems of miniaturization of spindle bearings by using fluid or hydrodynamic bearings. Such bearing designs could potentially reduce parts, permit greater speeds, and enhance shock resistance of spindle bearings. However, oil containment in such a limited space is a major problem which has yet to be completely overcome. Additionally, proper operation of a fluid bearing requires continuous, high speed rotation. Disk spindles, which typically rotate at high constant speed, may become suitable applications. But a rotary disk actuator typically moves back and forth in a short arc. The motion of a disk actuator would generally not produce sufficient fluid pressure to support a fluid bearing, and fluid bearings would therefore be unsuitable for disk actuator assemblies.